Skin aging is a complex biological process affecting various layers of the skin, but whose major effects are seen in the dermis. There are two biologically independent aging processes that occur simultaneously. The first is intrinsic aging, which affects skin as well as, most likely, the internal organs. The second is extrinsic aging or photo-aging which is the result of exposure to the elements, primarily ultraviolet irradiation. The consequences of innate aging can be observed all over the skin, including areas protected from the sun. In the areas exposed to the sun, particularly the face and the backs of the hands, photoaging damage is superimposed to tissue degeneration due to innate aging. Thus, the most noticeable changes on facial and neck skin, the primary areas that patients are concerned about, result from the combination of intrinsic and extrinsic aging processes. It has been suggested that as much as 80% of facial aging may be ascribed to exposure to the sun, although other factors (i.e. cigarette smoking) can contribute to premature wrinkling.
From a biochemical standpoint, photoaging is thought though to be induced mainly by: some proteases, mainly metalloproteases, which are overproduced and overrealesed by keratinocytes and fibroblasts as a consequence of the interaction with ultraviolet radiation (these proteases are degradative enzymes irreversibly damaging collagen, elastin and hyaluronic acid, bringing about dermis scars and visible wrinkles); and by oxidative stress, able to eliminate the normal skin antioxidant defenses in a very short time.